In Situ Soil Vapor Extraction for the Remediation of Volatile Organic Compoundsin the Vadose Zone

Presented by: Stephine Smith

April 15, 2016

The Road to RecoveryModern Day Lifestyles are Energy IntensiveAs Global Populations RiseEnergy Demand Grows ExponentiallyHarvesting, Production and Disposal of Resources Inadvertent Contamination• Air• Soil• Surface and groundwaterFuel Sources : Petroleum and NuclearHazardous Waste: Poses Threats to Human Health and the Environment

Chief Contaminants in Soil

1. Volatile Organic Compounds / Semi Volatile

2. Inorganic Compounds (heavy metals/radioisotope)

3. Mixed Contaminants (organic + radioisotopes)

4. Pathogenic (bacterial or viral)

Physical, Chemical, Biological Properties • Contaminant• Soil MatrixGovern the fate, behavior and transport of constituents

Due to the complex aspects of each it is important to select the appropriate remediation technique

Rules and Regulations

DOE not a regulatory bodyDOE O 435.1 Office of Environmental Management is sanctioned to self-regulate nuclear wasteTogether with EPA they issue

• Clean Up Standards • Regulations • Guidance Documents

There are several phases before appropriate remediation techniques is selected

Remediation Phases• Discovery• Investigation• Site

characterization• Feasibility study• Laboratory testing • Pilot testing• Design• Installation

• Start up • Operation• Maintenance• Monitoring• Site closure plan• Clean up goals

• Decrease volume, mobility, toxicity

• Future land use

Goals and Future Land UseComplete removal at any site is impractical due to economically inefficiency

Considerations of future land use and potential receptors will aid in setting an acceptable level of contamination

Receptors: Frequency and Duration• Resident – most stringent (12 hr./day 350 days/yr.)• Worker - least stringent (8 hr./day 250 day/yr.)• Construction Worker• Recreator

Determines extent of clean up effort

Site CharacteristicsDetermine Techniques UsedChemicals of Interest• VOC’s contain carbon• Volatilize at standard temperatures

Once released• Sorbed onto soil particles• Migrate through soil to ground water

Infiltration• Oily liquid • Non-polar molecule • Interact weakly• Low interfacial tension• Form NAPL’s

Non-Aqueous Phase LiquidsDo not readily dissolve in water• LNAPL’s < H2O Float• DNAPL’s > H2O Sink to sediment

Remediation TechniquesIn Situ vs. Ex Situ

In Situ: materials in place > cost efficient for timely remediation

Requires greater understanding of soil physics

Access appreciate remediation strategy

Pore Space Dominates Wetting front of water wicked into the micro-poresNAPL’s are repelled by soil moisture into the macro-pores displacing air Until low permeability

Soil Physics

Contaminant and Soil PropertiesPartitioning and Diffusion in Soil

• Soil intrinsic permeability

• Porosity• Moisture content• Hydrogeology• Preferential flow

patterns • Moisture gradient

SVE preferred

Soil Vapor Extraction

Conventional: cost and performance are establishedOil Industry since 1934 for EOC

Only works VOC’s in Vadose Zone (unsaturated)• Vertical wells placed around contamination• Blower attached to extraction well at the

surface• Induces air flow through the soil matrix• Vacuum causes VOC’s, SVOC’s and soil

moisture evaporate / volatilize upward through profile

• Collected at the surface • Contaminated air is passed through a

liquid/vapor separator to remove water vapor before treatment

https://www.youtube.com/watch?v=z_g8wVSwJl8https://www.youtube.com/watch?v=cxhOfpPKK1g

SVE ApplicationsCaps and Covers (concrete, asphalt, geo-membranes)Vertical wells are the most widely usedHorizontal wells applied to provide better lateral flow**Ground water flow models - preferential gas flow pathwaysBest Suited • Well drained soils • High permeability• Low organic carbon contentCost effective and efficient• Pilot Program 10 – 40 K $• Average cost 10 – 60 $/ft3

Leads to increased soil aeration and oxygen contentPromoting biodegradation (bioventing)

Capillary FringeSeasonal fluctuations Pulls contaminants into and below water table

DNAPL’s > H2O sink Beyond SVE capabilities

In Situ Air SpargingInnovative approachAddresses contamination in and below the water tableUsed in Europe since mid-1980’sInfancyInjecting air below the water tablehttps://www.youtube.com/watch?v=OBbMqizYND4

Contaminants dissolved in water and sorbed to soil particles partition into an ADVECTIVE air phase Stripping contaminants for the media transporting upward through the soil matrix into the vadose zone where they are collected by SVE

Increases removal rates Site cleaned up faster Overall Economic Efficiency

ConsiderationsSVE • Heterogeneous soils• High organic carbon• Low permeability Increasing time Driving up price

IAS• Infancy• Poses risks not associated with other technologies• Important Monitoring• Assure injection pressures and flow rates are appropriate

for soil• Excessive migration of gases outside area of influence• Plume can migrate• Previously immobile constituents become mobile

Final ThoughtsThorough consideration must be given to soil physical properties

• Soil Temperature• Moisture Content• Porosity• Sorption• Partitioning• Soil Texture• Permeability

ALL play a vital role in selecting the appropriate remediation technique

Works CitedEPA: Office of Solid Waste and Emergency Response• In situ Treatment Technologies for

Contaminated Soil

DOE: Office of Environmental Management

Groundwater Monitoring and Remediation Journal• Johnson et., al 2007• Marley et., al. 2007

Environmental Soil Physics• Daniel Hillel Appendix II

Vadose Zone: Science and Technology Solutions• Brian Looney, Volume II

Additional InformationThe Risk Assessment Information System (RAIS)• Database • Developed by The Institute for Environmental

Modeling (TIEM)• Within the University of Tennessee Knoxville

(UTK)• Funded by DOE• Housed in ORNLProvides free resources that aid in accessing a sites extent of contamination

Assist DOE / EPA in setting Clean Up Standards

For more info on this free resource please visithttps://rais.ornl.gov